Has Fermi glimpsed dark matter?

New results from NASA's Fermi Gamma-Ray Space Telescope appear to confirm a larger-than-expected rate of high-energy positrons reaching the Earth from outer space. This anomaly in the cosmic-ray flux was first observed by the Italian-led PAMELA spacecraft in 2008 and suggests the existence of annihilating dark-matter particles.

Physicists believe that about 80% of the mass in the universe is in the form of a mysterious substance known as dark matter. Unable to observe dark matter using light or other forms of electromagnetic radiation, researchers are attempting to find direct evidence of it on Earth using either heavily shielded underground detectors or with particle accelerators. But they also have a third, less direct, option – using satellites or balloon-based instruments to detect the particles that some theories predict are created in space when two dark-matter particles collide and annihilate.

The Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA) mission caused excitement in 2008 after it found significantly larger numbers of positrons (anti-electrons) at energies 10–100 GeV than expected. Taking into consideration only positrons produced when protons interact with the interstellar medium, physicists had calculated that at higher energies there should be a gradual drop in the number of positrons reaching the Earth. However, dark-matter collisions are expected to produce equal numbers of electrons and positrons over a given energy range. This would boost the ratio of positrons to electrons detected because positrons are substantially less abundant than electrons in the universe as a whole.

Positrons or protons?

The PAMELA results, however, were not watertight, mainly because of the possibility that the mission was confusing positrons with the far larger numbers of protons reaching its detectors. But the latest results from Fermi appear to remove these doubts. Although it is a gamma-ray telescope, Fermi in fact works by detecting electron–positron pairs and so is also well suited to studying cosmic rays. Unlike PAMELA it does not include a magnet to distinguish between electrons and positrons, but the Fermi scientists realized they could use the Earth's magnetic field instead. This bends electrons and positrons in such a way that certain patches of the sky will contain just one kind of particle but not the other. So by totting up the signals coming from these regions, the researchers were able to separately measure the electron and positron fluxes, and hence work out the fraction caused solely by the latter.

The team observed a significant increase in the positron fraction at higher energies. This coincides with the PAMELA results, to within the errors on the Fermi measurements.
The results of this analysis were presented at a conference in Rome last week by Fermi collaboration member Warit Mitthumsiri. Mitthumsiri's colleague Stefan Funk of the SLAC National Accelerator Laboratory in California believes that the results constitute "a very nice confirmation" of the observations from three years ago, and maintains that the background noise has been properly accounted for. "There will be a small fraction of protons that will look like electrons," he says, "but we are quite positive that we have subtracted that fraction correctly."

PAMELA's principal investigator, Piergiorgio Picozza of the University of Rome Tor Vergata, agrees. He says that, barring some unknown source of protons, the Fermi results "strongly support the positron excess at higher energy", adding that the agreement is all the more compelling because the two data sets were derived using "different analysis, different detectors, and completely different experimental conditions".

We can confirm the PAMELA result but it is still puzzling where these additional positrons come from Stefan Funk, SLAC

However, even if the results themselves are now on a firmer footing, their interpretation is still open to debate. In principle, the positron excess could point to a misunderstanding in how protons interact with the interstellar medium, but Funk believes that it is unlikely. What is more likely, he says, is the existence of some other, primary, source of positrons, but that could be either annihilating dark-matter particles or some more mundane astrophysical process, such as acceleration by pulsars. "We can confirm the PAMELA result," he explains, “"but it is still puzzling where these additional positrons come from."

AMS or Planck could provide answers

John Wefel, an experimental astrophysicist at Louisiana State University in the US, believes that the Alpha Magnetic Spectrometer (AMS) could help to establish what is causing the excess. The AMS has just become operational on the International Space Station and Wefel points out that it has a more powerful magnet than PAMELA and will therefore be able to probe positron fluxes at higher energies. "What AMS 'sees' may be very important in deciding between different models," he says.

Neal Weiner of New York University believes instead that NASA's Planck mission might provide the answer; he argues that if the positron excess really is due to dark-matter annihilation, then that annihilation should alter the cosmic microwave background. "Some people will jump and say this is clearly dark matter, and some will dismiss this as messy astrophysics," he says. "But I think both reactions miss the point. This is science after all, so no-one's gut feeling is really the question – we simply need more data, and we shall have more data."

Reached a basic limit

Hi but the CMBR map that was taken before can be compared analysed by taking the microwave and positrons together we can get two things1.dark matter properties2.true picture of the universe after the Big Bang.

so we have reached fundamental properties of dark matter and also the bigh bang.

Right on

"WIMP" proponents are getting quite desperate after 35 years of expensive No-Shows.Great, succinct criticism of this unending dark matter hunt. There has to be some one among the unrelenting WIMP proponents will finally realize the strong similarity between the hunt for the dark matter and the hunt for the aether. But I guess the hunt for the aether did not really ceased until a decent theory came along that made that hypothetical construct "superfluous"--a word Einstein used in his 1905 paper. There is only one theory that is going to finally put an end to this lucrative dark matter hunt and that is my theory. But who is going to believe that. For one, you do not believe it. But would you if someone replicated my experiments where a ~10% increase and a ~5% decrease in the test mass has been observed. Pardon the self promotion. But with experiments and not apt phrases is the only way I know how to stop the this 70 year-old hunt.

Dark Matter Identified?

If anyone out there wants a scientific identification of the dark matter, and one with empirical evidence to back it up, rather than unobservable fantasy particles or crackpot pseudo-science, then here is what you can do.

Which Mysteries Might MACHOs and PLANCHOs Solve?

The recent discovery of an estimated 400 billion unbound planetary-mass objects in the Galaxy, and previous evidence for stellar-mass microlenses, prompt the following comments.

If the Galaxy has huge populations of unbound ultracompact objects with masses in the 0.1 to 1.0 solar mass range (MACHOs) and Neptune/Jupiter mass range (PLANCHOs), then several key astrophysical enigmas might be solved by their existence. A partial list of those mysteries that MACHOs and PLANCHOs might explain would include the following.

The composition of the galactic dark matter

The ubiquitous 1-100 day variability of quasars

The factor of 6 excess in the ARCADE 2 radio background observations

The origin of cosmic rays

The composition of the recently discovered infrared-faint radio transients

A significant unidentified component of the X-ray background

A significant unidentified component of the Gamma-ray background

Ubiquitous Gamma-ray burst phenomena

The origin of ubiquitous unidentified optical transients

It would seem prudent at this point to put as much effort into the dark matter search for “primordial” Kerr-Newman ultracompact objects as has been expended in the unsuccessful 35-year effort to find any form of “WIMP” or exotic particle dark matter.

Dark matter is gravitational energy

This rresearch shows how dynamic gravity agrees exactly with the general theory of trelativity at low and medium mass densities but at high maas densities sucha s black hole the the extra gravitation acts as " dark matter" [1]. Dark energy also drops out [2].

Dark matter is a pure invention to save GR failure and consequently it doesn'y exist since Eisntein whole theories are absolutely FANTASIA.The BIg Bang a simple tale for children tha now it is converted to a simple religion, the shame of the Human Race.See, please: autodynamicslborg.bl…See, please: autodinamicaar.org…Lucy Haye PH. D.

Hi but the CMBR map that was taken before can be compared analysed by taking the microwave and positrons together we can get two things1.dark matter properties2.true picture of the universe after the Big Bang.

so we have reached fundamental properties of dark matter and also the bigh bang.

How sweet it is>

One never tires of the "everybody is out of step but me" theories that so often appear in these comments. So often the tone of the remarks seems to smack of some sort of emotional desperation. At any rate, time will (as it usually does) tell as we develop and deploy more and more sensitive technologies to observe our always surprising universe.

And who knows, perhaps will give us some idea if ours is really the "only" universe at that.